Space vector pulse width modulation (SVPWM) and selected harmonic elimination PWM (SHEPWM) are applied simultaneously in the PWM process of AC speed regulation system. SVPWM is adopted at low frequency and SHEPWM is used at medium frequency. This hybrid modulation method avoids the problems of large storage of SHEPWM at low frequency and variation of SVPWM harmonic characteristics at medium frequency. A zerocrossing point switching method is proposed for harmonic current switching, which guarantees the smooth transition of switching angle number from 5 to 1 in SHEPWM technology. In the switching process from SHEPWM to SVPWM, a reference voltage vector inphase switching method is adopted to achieve smooth transition. Simulation results prove the validity of the theory.